One of the chief appeals — not to mention requirements — of crime fiction is a fundamental reliance on reason.

Sure, characters may be wicked, questing, sad, madly eccentric. Plots can be as twisted as DNA strands. Tone and writing may range from pedestrian to dazzlingly, brilliantly taut.

But ultimately a piece of crime fiction, however closely it creeps to the edge of unreason — and a lot of tales do exactly that — doesn’t work properly if it topples right over.

That toppling can take several forms, one of which is a discernible slide from drama into melodrama. The Second Sister, for all its potential popularity in theme and plot, is one of those. Too much emotion (or sentiment), not enough reason.

Of course, not everyone will object to that sort of thing, so Claire Kendal, born in the U.S. but a long-time resident of England, will likely do reasonably well with her long tale of two sisters, separated in age by a decade, the older one long-vanished, the younger obsessed by learning what happened to her.

Soon after her son Luke, now 10, was born, Miranda disappears, aged 30. Now her sister Ella has turned 30. She’s a doting aunt to the precocious Luke, a prickly daughter to her protective, traumatized parents, and a university drop-out who teaches fierce self-defence techniques to women who’ve been battered or sexually assaulted.

She has an insanely hostile, jealous woman “friend,” a loyal cop who was her best buddy in childhood and her first lover, grief that appears to have paralyzed her development since Miranda vanished, and a desperate, renewed fervour to learn what happened.

Given her adoration for her infant son, it seems impossible Miranda took off voluntarily. It’s heartbreaking to think she was taken and remains somewhere, somehow alive. And heartbreaking also to recognize that she’s almost certainly dead, almost certainly murdered.

That last probability is resurrected when tabloid newspapers report phone messages finally have been tracked that link Miranda to a sadistic serial killer, Jason Thorne, long locked away in a psychiatric hospital for the exceedingly unpleasant killings of at least three other women.

Thus, against the advice of just about everyone, Ella decides she must meet Thorne to see if she can wangle a confession, or at least a sense of whether he was involved in whatever happened to Miranda.

Although the shrewd and brutal Thorne has refused all other attempted visitors to his high-security ward, he’s pleased to sit down with her.

All that might be perfectly acceptable and comprehensible crime fiction drama. So would the fact that Ella maintains a silent running conversation with Miranda, and that their mother insists, pitifully, on everyone referring to Miranda in the present tense.

What is immediately inexplicable is why Ella has stayed friends since childhood with a deeply malevolent woman, why she is cruelly self-centered when it comes to her sorrowful mother, or why she is instantly prepared to ricochet from affectionate dependence to bitter mistrust when it comes to her first lover, the cop with whom she generally seems to envision a future.

As she delves further into Miranda’s life, it becomes clear either she didn’t know a whole lot about her older sister, or wasn’t troubled by her less attractive aspects. Nevertheless, she and the novel pound and wind their way through an assortment of increasingly fraught events, motivations, and judgments.

When it comes to the conclusion, picture the sort of silent movie melodrama that featured a moustache-twirling villain and a wide-eyed, menaced maiden. With, of course, rescue and resolution arriving on the scene in the very nick of strangely old-fashioned time.